The present invention relates to a coating method and, in particular, to a coating method that is capable of effectively preventing the occurrence of troubles due to deposition of dust and dirt in a support transport line on rollers.
The conventional process for the production of photographic paper and films on a large scale consists of transporting an elongated strip of support over many rollers of various types so as to form a coating of emulsion or other components on the support and slitting the coated web into desired sizes. The length of the transport line used in this method will, of course, depend on the size of the plant in which it is housed and, in an extreme case, the transport line may extend as long as several hundred to several thousand meters and requires no less than 10.sup.3 -10.sup.4 rolls.
The production line is operated in a strictly controlled environment so that the buildup of dust and dirt is held to a minimum but it has been impossible to avoid fragments of the support itself, which may be in the form of paper or plastic particles, from being brought into the line. This problem (i.e., dust or dirt buildup due to paper or plastic particles) becomes pronounced if the line speed is increased in order to comply with the growing demand for photographic paper and films and to meet the requirements of modern plants such as a lower production cost. If dust or dirt sticks to the back side of the support during coating operations, the affected areas of the support will protrude upwardly and cause unevenness in the layer formed by continuous coating. This "streaking" phenomenon is fatal to the final product and the yield of commercially acceptable products is accordingly decreased.
Conventionally, such dirt and dust are removed by manual clean-up operations during periodic shutdowns but this method has the disadvantage that complete clean up of areas of limited access is not possible and that it is quite time-consuming. Because of these problems, manual cleanup operations have not been conducive to achieving a high production rate and a low production cost.
A particular problem arises durig the cleanup of a production line employing grained rollers having fine asperity on their surface; that is, the dirt, dust or any other foreign matter that has been trapped in cavities in the surface of a grained roller cannot be readily removed by routine cleanup procedures. Grained rollers are chiefly used in areas where a travelling elongated support is likely to be subjected to local load for the purpose of stabilizing the overall support transport line. If one wants to speed up the production line, it is essential to incorporate grained rollers in selected portions of the transport line.
The present inventors made concerted efforts to develop a coating method for applying a coating layer on at least one surface of an elongated support that travels continuously as it is transported on rollers in the production of photographic paper and films. As a result, the inventors have devised a system wherein an adhesive layer is formed in selected areas of one surface of the support in contact with the rollers; this system is operated in such a manner that no coating layer is formed in those areas of the support being transported which have the adhesive layer, whereas a coating layer is formed in those areas of the support which have no adhesive layer. The product attained by this coating method does not experience any of the trouble that would otherwise be caused by transfer of dust or dirt from the roll surface. In addition, the rollers can be readily cleaned up within a short period of time without suspending the flow of the production line.